The present invention relates to an impregnated flat seal made of an impregnable material, particularly an impregnated cylinder head gasket made of an asbestos fiber fabric, which may be metal reinforced, wherein the saturating agent is only partially hardened until it reaches a still plastically deformable consistency.
Cylinder head gaskets such as those disclosed in U.S. Pat. No. 4,201,804 are saturated with hardenable saturating agents to improve their operating characteristics. In order for these gaskets to be able to adapt themselves, when installed, to the unevennesses of the sealing faces of the associated cylinder head and engine block when under sealing pressure, the hardening of the impregnating agent is stopped when it reaches a still plastically deformable consistency, i.e. the impregnating agent is only partially polymerized. In the installed state, under the operating heat of the engine, the impregnating agent undergoes its final hardening so that the gasket will then attain its full functioning capability.
In practice it is customary to attain the desired degree of partial hardening by means of additives known from the plastics or rubber art which are added to the impregnating agents. This is done either by a preliminary impregnation of the soft material plates with solutions of the additives, or these substances are added directly to the impregnating agents. For example, the polymerizable and cross-linkable liquid saturating agents disclosed in U.S. Pat. No. 4,201,804 receive additions of aging protectants whose concentration causes the polymerization process to be stopped at the desired points by way of a chain breakoff reaction, to thus arrive at the desired degree of partial polymerization. Due to their good plastic adaptability, the gaskets produced in this way have been found to be excellent when used in mass-produced engines.
The use of these gaskets as replacement parts for repairs is fraught with problems, however. It has been found that the saturating agent slowly hardens during storage periods customary for the use of the gaskets as replacement parts, so that the gaskets, when stored over a long period of time in a repair facility, may gradually lose their plastic adaptability to the unevennesses of the sealing faces of the cylinder head and engine block in which they will be installed. It has been attempted to overcome this drawback by the addition of larger quantities of the additives which stop the polymerization process. However, these measures were not successful and, in principle, they even brought about poorer results since the larger quantities of additives again unfavorably influenced the strength characteristics of the hardened saturating agents.